The LTE network is composed of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) base stations, namely Evolved Node B (eNB), and an Evolved Packet Core (EPC) of the evolved packet switching center. The coverage range of the LTE system is composed of cellular cells dominated by a plurality of eNBs.
When one user moves in the cellular cell system, the user will unavoidably move from one cell to another cell, which causes the cell re-selection or cell handover. One simple example is that, when one user is calling and moves from the coverage range of a certain cell to the coverage range of another cell, the user is required to automatically carry out handover between cells for the purpose of not interrupting the call. This process is carried out without acknowledge by the user, and with no need of the user involving. As for to which cell the user hands over, and when to carry out the handover, they are all selected by the network side. The handover can include the intra-cell handover, inter-cell handover in the eNB, inter-eNB handover, and the handover between different access systems and so on according to the belongings of the both previous and posterior cells related to the handover. Without loss of generality, the handover procedure can refer to the procedure of the inter-eNB handover, with reference to FIG. 1, comprises:
step 101, the User Equipment (UE) provides the downlink measurement result report to the serving eNB1;
step 102, the eNB1 makes the handover selection, and completes the handover preparation procedure along with eNB2 at the target side of the handover;
step 103, the eNB1 notifies the UE to carry out the handover through the signaling;
step 104, the UE carries out the handover to the eNB2 according to the signaling.
Wherein the procedure of handover selection at the network side in step 102 is required to synthetically consider many factors, wherein the most important factor is the measurement report of the UE in step 101, and when the serving signal quality of local cell is lower than a certain threshold and after the signal quality of a certain neighbor cell reported by the UE is higher than a certain threshold, the network side can notify the UE to carry out the handover. However the network side also should obtain some other assistance information as the reference against some abnormal cases occurring, for example, the network side should include the history information of the UE, such as the time that the UE stays in the last cell in the process of the calling or the traffic, during the handover, to avoid the occurrence of the Ping-Pong handover.
However, in the current handover, a plurality of abnormal cases are unavoidable, for example, the Radio Link Failure (RLF) occurs in the target cell soon after the UE carries out the handover, thereby affecting the system performance, and also affecting the user's experience. Wherein, one of the reasons is that the uplink transmission by the UE in the target cell is not ideal. The main factor considered in the current handover selection is obtained according to the measurement of the downlink serving signal of the neighbor cell by the UE.
Besides, in the LTE system, in order to reduce the amount of the manual maintenance work of the network and to optimize the network capability, the LTE is required to support the Self-Organized Network (SON) function in the demands proposed by the Next Generation Mobile Networks (NGMN) organization at present, and the SON function includes the Coverage and Capacity Optimization (CCO) function of the network, namely the parameter configuration of the cell can be automatically modified through the automatic configuration function and the self-optimization function of the network, thereby achieving the optimization of the network coverage.